Detection and estimation of anions have received considerable attention for their important roles in biological, industrial, and environmental processes. In particular, cyanide is a highly toxic anion for living system. However, cyanide is widely used for industrial applications, which releases cyanide into the environment as a toxic contaminant. The World Health Organization (WHO) has set the maximum contaminant level (MCL) of cyanide in drinking water to be 1.9 μM (0.04 ppm) and a greater content can have acute effects. This is of paramount importance particularly after the accidental cyanide spill in Romania in the year 2000 which is considered to be one of the worst disasters in Europe since Chernobyl. The detection of CN− is also important since many plants and fruits are known to contain cyanides. Most of the reported probes are colorimetric or fluorescence dosimeters (indicators), useful for the one time detection of the analyte. References may be made to: a) Guidelines for Drinking-Water Quality, World Health Organization: Geneva, 1996; b) Ullman's Encyclopedia of Industrial Chemistry, Wiley-VCH: New York, 1999; c) G. C. Miller, C. A. Pritsos, Cyanide: Social Industrial and Economic Aspects; Proceedings of the TMS Annual Meeting, 2001 pp 73-81; d) R. Koenig, Science, 2000, 287, 1737; e) A. W. Hayes, Principles and Methods of Toxicology, 5th ed. Taylor and Francis, Boca Raton, Fla.
The main disadvantages which have prevented the practical application of molecular probes for the detection of metals ions especially, potentially dangerous anions such as cyanide, in aqueous media at normal conditions are;
1) that the detection requires professional laboratory type operations, such as precise transfer of solutions, usage of sophisticated instrumental techniques etc., making it less useful to people who do not have any scientific background.
2) the low sensitivity and selectivity of the probes towards cyanide anions for an instrument free observation. For example, a probe which can distinguish analyte binding by color change or fluorescence change with naked eye.
3) compatibility of the probe in aqueous conditions and at the same time it should interact with cyanide anions in solution. An ideal fluorophore must have comparatively good quantum yield under aqueous conditions.
4) The fourth and significant one is the difficulty in reprocessing and thereby multiple use of the probe.